The drill string utilized in drilling a well typically includes a drill bit at the bottom, a set of drill collars above it which are heavy wall pipe to impart direction control in drilling the well and a string of drill pipe which extends to the surface. The drill pipe is rotated, and, of course, the rotation is imparted to the full length of the drill string. Sometimes, a hole drifts slightly and carries the drill string into contact with the side of the hole. Sticking can occur, for instance, when the drill string forms or cuts a key seat, and it can also be occasioned by differential pressure sticking. Without regard to the cause, sticking is a common problem. Sticking is a problem which often requires in-place disassembly of the drill string. It may be necessary, as an example, to retrieve the drill pipe, but leave the drill collars and drill bit in the hole. They are left for a subsequent fishing trip. While sticking can typically occur at any place along the drill string, but ordinarily occurs at the drill collars, remedial steps typically begin by unthreading the drill pipe from the drill collars.
This is ordinarily accomplished through the use of a safety joint. A drill string is threaded by rotation to the right so that drilling via rotation in the same direction continually tightens the threaded connection from joint to joint. Reverse rotation occurs, but is relatively rare. The present invention is a safety joint which enables disconnection without running the risk of accidental unthreading at some other threaded connection in the drill string. In safety joints where rotation in the reverse direction is required to unthread the drill string, the risk of unintended unthreading at some other joint is quite great. Occasionally, it is necessary to rotate to the left, and accidental unthreading occurs from time to time as a result of rotation to the left. This failure of prior art safety joints has been overcome by the present disclosure.